1. Field of the Invention
The present invention relates to technology for controlling the fuel pressure supplied to fuel injection valves of an engine. More particularly, the invention relates to technology for properly controlling the fuel pressure during an engine stop according to the environment.
2. Related Art of the Invention
In order to prevent a rise in the temperature of fuel caused by excess fuel to be returned into a fuel tank from a pressure regulator, there has been proposed a system as fuel supply device of an engine constituted such that no pressure regulator is provided but, instead, a sensor is provided to detect the fuel pressure in a fuel supply passage, a discharge amount of a fuel pump is controlled according to the fuel pressure detected by the sensor to obtain a required fuel pressure that meets an engine operation condition, so that the discharge amount of the fuel pump is brought into agreement with a required fuel amount to suppress the production of excess fuel (Japanese Unexamined Patent Publication No. 7-293397).
According to this device for supplying fuel, when the engine operation is stopped, as a result that the operation of the fuel pump is stopped, the fuel pressure remaining in the fuel supply passage downstream of a check valve for preventing the return of fuel becomes a value feedback controlled by to a target fuel pressure during the operation (usually, idling) just before the stop of engine operation.
When the engine operation is stopped after the engine has been warmed up and then, the engine is restarted after about one to two hours have passed, however, demands on the fuel pressure to obtain favorable startability of the engine conflict with each other depending on the environmental conditions of the engine.
That is, under a heat-resisting wherein an engine environmental temperature (atmospheric air temperature, water temperature when the engine operation is stopped, and ultimately, fuel temperature) is high, the fuel in the fuel supply passage is vaporized to generate vapor and the required fuel amount is not injected at the restart of the engine, resulting in that an air-fuel ratio becomes lean deteriorating the startability. In order to prevent vaporization of the fuel, therefore, the fuel pressure is required to be raised.
Under an ordinary engine environmental temperature condition (atmospheric air temperature of up to about 25xc2x0 C.), on the other hand, when the fuel in a large amount is leaked out through a nozzle hole of the fuel injection valve during the engine is not in operation, the air-fuel ratio becomes too rich at the restart of the engine to deteriorate the startability. In order to prevent the leakage of fuel, therefore, the fuel pressure is required to be lowered.
So far, the target fuel pressure during the idling operation that is usually carried out just before the engine operation stop has been set to an intermediate value of the above described respective required fuel pressures, failing to satisfy neither requirements to a sufficient degree. Besides, since the fuel pressure has been set to be higher than a fuel pressure required during the idling operation, a difference in the fuel pressure occurs relative to the operation region near the idling operation. Therefore, the operation performance is lost due to a delay in the fuel pressure feedback control, and the fuel economy becomes poor due to an increase in the force for driving the fuel pump.
There has further been proposed a system equipped with a pressure regulator to control the fuel pressure to be constant during the engine operation, wherein the fuel temperature is detected at the time when the operation is stopped, and the fuel pressure is lowered by opening the relief valve when the fuel temperature is so low as will not generate vapor (Japanese Unexamined Patent Publication No. 9-42109). With this system, however, it is difficult to accurately adjust the fuel pressure and, besides, the adjustment is accomplished only in a direction to lower the fuel pressure (to prevent the leakage of fuel).
The present invention was accomplished by giving attention to the above problems in the conventional technique, and has an object of accomplishing a favorable restartability by properly adjusting the fuel pressure at the time when the engine operation is stopped.
Another object is to easily adjust the fuel pressure by a control operation similar to that of during the engine is in operation.
A further object is to properly adjust the fuel pressure over a wider range.
A still further object is to more properly set the fuel pressure during the idling operation accompanying the adjustment of the fuel pressure at the engine operation stop.
In order to accomplish the above-mentioned objects, the present invention is basically constituted as described below.
During the engine is in operation, the drive of a fuel pump is feedback controlled so as to accomplish a target fuel pressure while detecting the fuel pressure supplied from a fuel pump to a fuel injection valve through a fuel supply passage equipped with a check valve.
It is detected that the engine operation is stopped, and the engine environmental temperature is detected during the operation is stopped.
Further, during the engine operation is stopped, by feedback controlling the drive of the fuel pump, the fuel pressure in the fuel supply passage is adjusted to reach a fuel pressure corresponding to the engine environmental temperature condition during the engine operation stop.
With this constitution, when the engine is in operation, the fuel pressure is feedback controlled to become a target fuel pressure to be set according to the engine operation condition while detecting the fuel pressure. When the engine operation is stopped, the engine environmental temperature condition during the engine operation stop is detected, and the fuel pressure is feedback controlled so as to reach a value corresponding to the environmental temperature condition.
In this way, after the engine operation is stopped, the fuel pressure in the fuel supply passage downstream of the check valve may be adjusted to be higher to suppress the vaporization of fuel under a heat-resisting condition that the environmental temperature is high, while the fuel pressure may be adjusted to be lower to suppress the leakage of fuel from the fuel injection valve under an ordinary condition that the engine environmental temperature is low. Thereby accomplishing favorable startability in either condition.
Further, when the engine is not in operation, the fuel pressure in the fuel supply passage may be adjusted by the feedback control to become a target fuel pressure during the idling operation, under a condition that the engine environmental temperature is equal to or lower than a set temperature, while, under the condition that the engine environmental temperature exceeds the set temperature, the fuel pressure in the fuel supply passage may be adjusted by the feedback control to become a heat-resistant target fuel pressure set to be higher than the fuel pressure during the engine is in operation.
In this way, when the engine environmental temperature during the engine operation stop is equal to or lower than the set temperature, the fuel pressure can be adjusted to the target fuel pressure during the idling operation to suppress the leakage of fuel from the fuel injection valve. When the engine environmental temperature during the engine operation stop exceeds the set temperature, on the other hand, the fuel pressure can be adjusted to the heat-resistant target fuel pressure set to be higher than the fuel pressure during the engine is in operation to suppress the vaporization of fuel, thereby improving the restartability. Besides, the target fuel pressure during the idling operation can be set to be lower without the need of giving consideration to the heat-resisting, thereby improving the operating performance and fuel economy.
Further, when the engine is not in operation, the fuel pressure in the fuel supply passage may be adjusted by the feedback control to become a target fuel pressure set to be lower than the fuel pressure during the engine is in operation after the fuel in the fuel supply passage is once drained by opening a relief valve connected to the fuel supply passage by-passing the check valve, under the condition that the engine environmental temperature during the engine operation stop is equal to or lower than the set temperature, while, under the condition that the engine environmental temperature during the engine operation stop is higher than the set temperature, the fuel pressure may be adjusted by the feedback control to become a heat-resisting target fuel pressure set to be higher than the fuel pressure during the engine is in operation.
Therefore, when the engine environmental temperature of during the engine operation stop is equal to or lower than the set temperature, after the fuel in the fuel supply passage is drained by opening the relief valve to lower the fuel pressure, the fuel pressure is adjusted to become the target fuel pressure set to be lower than the fuel pressure during the engine is in operation by taking into consideration a rise in the fuel pressure due to an increase in the temperature during the soaking, so that the leakage of fuel from the fuel injection valve can be more efficiently suppressed to thereby further improve the restartability. When the engine environmental temperature during the engine operation stop exceeds the set temperature, further, the fuel pressure is adjusted to become the heat-resisting target fuel pressure set to be higher than the fuel pressure during the engine is in operation, thereby suppressing the vaporization of fuel to improve the restartability.
Further, the engine environmental temperature may be detected by a detection value of an engine cooling water temperature or by a value obtained by adding a detection value of an intake air temperature or an on/off detection value of an air conditioner to the detection value of the engine cooling water temperature.
When a detection value of a water temperature sensor which is essential for controlling the engine is used, the engine environmental temperature condition can be easily detected without increasing the cost, and further, the engine environmental temperature condition can be detected more accurately if the detection value of the intake air temperature or the on/off detection value of the air conditioner is added to the detection value of the engine cooling water temperature.
Further, the engine environmental temperature condition may be detected by detecting the fuel temperature.
In this way, it possible to most accurately detect the engine environmental temperature condition for adjusting the pressure of the fuel.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.